Suction strainer with a internal core tube

ABSTRACT

A suction strainer includes a hollow internal core tube and an external filtering surface built around the internal core tube. A plurality of openings are defined through the side wall of the internal core tube core. In some cases the openings through the side wall are constructed and arranged such that there is somewhat less open area near the downstream end than the upstream end of the internal core tube, and the amount of open area tapers between the upstream end and the downstream end. As a result, when liquid is drawn into the internal core tube through the plurality of openings, a substantially uniform inflow distribution may be defined along substantially the entire length of the internal core tube. The internal core tube functions as a rigid structural support for the external filtering surface, enabling the apparatus to withstand post-LOCA hydrodynamic forces. The size of the filtering surface is enlarged by virtue of the fact that the filtering surface defines a plurality of filtering disk assemblies that are connected to and extend radially from the internal core tube. A separation distance is defined between neighboring disk assemblies, and filtering inner walls connect between neighboring disk assemblies and extend around the internal core tube at a radius less than the outermost radius of the disk assemblies. The total flow surface area is increased within a limited geometric profile. This serves to maximize surface area while minimizing post-LOCA reactive forces on attachment ECCS piping in a BWR suppression pool.

This application claims the benefit of U.S. Provisional application Ser. No. 60/003,266, filed Aug. 24, 1995.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of suction strainers, and more particularly to the field of suction strainers employed in the suppression pools of boiling water reactor (BWR) nuclear power plants.

A suction strainer employed in a suppression pool removes solids from a flow of liquid (e.g., water) being drawn into an emergency core cooling system (ECCS) pump. The flow of water is drawn through the suction strainer and then into the suction line of the ECCS pump. Employment of suction strainers is desirable because solid debris drawn into the suction line of a pump can degrade pump performance by accumulating in the pump or its suction or discharge lines, or by impinging upon and damaging internal pump components.

While almost any pump degradation can be characterized as being costly, the degradation of ECCS pump performance at BWR nuclear plants can be detrimental to safe plant shutdown following a loss of coolant accident (LOCA). At a BWR nuclear power plant following a LOCA, it is critical for the ECCS pumps to operate for an extended period of time in an undegraded fashion. In one mode of operation, the ECCS pumps are operated to recirculate water from the suppression pool back to the reactor core for the purpose of core cooling. A LOCA results from a high pressure pipe rupturing with such great force that large quantities of debris, such as pipe and vessel insulating material, and other solids, may be washed into the suppression pool. Conventional ECCS suction strainers currently installed in BWR plants would have a tendency to become clogged by such debris due to their small size and poor design. Also, when the large pressure pipes rupture with great force, suction strainers in the suppression pool are subjected to great hydrodynamic forces that can damage the suction strainers as well as subject the attachment recirculation piping to large reactive forces. These structural considerations, and space constraints, limit the size and shape of suction strainers in suppression pools.

Conventional BWR plant suction strainers are typically constructed and arranged in a manner such that, under full flow conditions, localized high entrance velocities are established through that portion of the suction strainer that is most proximate to the suction line of the pump, while low entrance velocities are established through that portion of the suction strainer that is more distant from the suction line of the pump. The high entrance velocities may draw more solid debris into contact with the suction strainer causing the portions of the suction strainer experiencing the high entrance velocities to experience higher head loss. As the portion of the suction strainer most proximate to the suction line collects debris, high entrance velocities are established at the portion of the suction strainer that is next closest to the suction line causing that portion to collect debris. This process often continues until the entire suction strainer has collected debris in varying quantities, resulting in a non-uniform build-up of debris on the outer surface of the strainer.

Localized high entrance velocities can be detrimental even when solids are not present in the liquid being pumped. For example, high entrance velocities can result in turbulent flow which tends to create greater pressure losses than laminar flow. Any such pressure losses reduce the net positive suction head (NPSH) available to a pump. As the NPSH available decreases, pump cavitation may occur. Similarly, localized high entrance velocities can cause vortexing. When a suction strainer is not sufficiently submerged, the vortexing can cause air ingestion which can severely degrade pump performance.

Attempts have been made to resolve certain of the problems associated with suction strainer-like devices in other applications. For example, cylindrical suction flow control pipes have been encircled with screen material and employed in water wells. Such wells typically employ a well pump above the ground surface and a riser pipe extending from the well pump to the water table. The suction flow control pipe is connected to the end of the riser pipe and extends further below the water table. Openings are defined through the side wall of the suction flow control pipe such that there is somewhat less open area near the riser pipe and somewhat more open area distant from the riser pipe. As a result, when water is drawn into the flow control pipe through the openings, a substantially uniform inflow distribution is defined along the length of the flow control pipe. While such suction flow control pipes offer some advantages, they are not suitable for all applications.

Attempts have been made, totally separate from flow control pipes, to increase filtering surface areas of BWR ECCS suction strainers in an effort to decrease pressure losses and thereby prevent pump cavitation. For example, such suction strainers may include a plurality of spaced, coaxial, stacked filtering disks. More particularly, such stacked disk suction strainers typically include an annular flange for attachment to the corresponding flange on the pump suction line. The stacked disk suction strainer provides an enhanced surface area and defines a longitudinal axis that is encircled by the attachment flange. A first disk is attached to the attachment flange. The first disk includes a pair of a radially extending, circular, disk walls, each of which encircle the longitudinal axis, and define a central hole. A first disk wall of the pair of disk walls is connected to the attachment flange. The first and second disk wall of the pair of disk walls face one another and are separated by a slight longitudinal distance. The first disk further includes an outer annular wall that encircles the longitudinal axis. The outer annular wall includes an annular first edge and an annular second edge. The entirety of the annular first edge of the outer annular wall is connected to the entire peripheral edge of the first perforated disk wall; and the entirety of the annular second edge of the outer annular wall is connected to the entire peripheral edge of the second perforated disk wall such that the pair of disk walls are connected at their periphery.

The stacked disk suction strainer further includes a plurality of inner annular walls that encircle the longitudinal axis, each of which includes an annular first edge and an annular second edge. The annular first edge of one of the inner annular walls is connected around the periphery of the central hole of the second disk wall. The annular second edge of that inner annular wall is connected around the periphery of the central hole of a disk wall of a second disk. The first and second disk walls, and the outer and inner annular walls are perforated and comprise the filtering surface of the stacked disk suction strainer. Additional perforated disks and inner annular walls are attached to one another in the above manner until the last disk is attached, wherein the outer disk wall of the last disk does not include a central hole. The stacked disk suction strainers may incorporate separate structural members to maintain the structural integrity of the stacked disk suction strainer. However, the conventional stacked disk suction strainers do not incorporate an internal core tube and related components, whereby the conventional stacked disk suction strainers are difficult to structurally reinforce and are susceptible to vortexing and the detrimental non-uniform localized entrance velocities discussed above.

There is, therefore, a need in the industry for an improved suction strainer.

SUMMARY OF THE INVENTION

Briefly described, the preferred embodiments of the present invention include a suction strainer that includes a filtering device with a strategically enlarged filtering surface and an internal core. The internal core is preferably in the form of an internal core tube, which is preferably an internal pipe with flow openings. In accordance with the preferred embodiments of the present invention, the internal core tube structurally reinforces the filtering device.

In accordance with the preferred embodiments of the present invention, the structural reinforcement provided by the internal core tube is enhanced by reinforcing structural members that extend radially from the internal core tube. The reinforcing structural members are preferably connected to and extend radially from and angularly around the internal core tube to structurally support the filtering surfaces of the external filtering structure. The internal core tube, in conjunction with the structural members, seeks to prevent air ingestion and vortexing. The suction strainer preferably extends away from the suction line of an ECCS pump to define a length, and in accordance with certain examples the preferred embodiments of the present invention, the internal core tube seeks to promote controlled inflow along the length to preclude the establishment of non-uniform localized entrance velocities through the filtering surface. In accordance with other examples of the preferred embodiments of the present invention, the internal core tube is not constructed to specifically promote such a uniform inflow along the length.

In accordance with the preferred embodiments of the present invention, the suction strainer is constructed in a manner that seeks to enlarge the filtering surface while minimizing the projected area of the suction strainer. The minimization of the projected area as well as structural reinforcement of the suction strainer enables the suction strainer to withstand high levels of hydrodynamic impact loading following a LOCA. The suction strainer also serves to minimize the bending moment and other reactive forces on the attachment ECCS piping in the BWR suppression pool.

In accordance with the preferred embodiments of the present invention, the filtering surface is defined by an external filtering structure that is attached to, extends from, and is built around the internal core tube and the reinforcing structural members. When the suction strainer is connected to the suction of a pump and submerged, a liquid flow path is established through the internal core tube and external filtering structure. The liquid originates exterior to the external filtering structure and is drawn through the filtering surfaces of the external filtering structure. The filtering surfaces separate solids from the liquid. The size of the filtering surface is enlarged by virtue of the fact that the filtering surface defines protrusions such that the distance that the filtering surface extends from the internal core tube alternates. The resulting enlarged filtering surface seeks to decrease average flow velocities through the filtering surface and thereby spread the collected solid debris in thinner layers, thereby decreasing overall pressure losses associated with the suction strainer. Once the liquid flows through the filtering surface, the liquid is drawn through the internal core tube and into the suction of the pump.

In accordance with the preferred embodiments of the present invention, the protrusions of the external filtering structure are in the form of a plurality of filtering plate assemblies that are connected to and extend radially from the internal core tube. Each plate assembly includes a pair of plate walls that face one another, define a distance therebetween, and are connected at their peripheries by an outer wall that surrounds the internal core tube. A separation distance is defined between neighboring plate assemblies. Inner walls connect between neighboring plate assemblies and extend around the internal core tube at a radius less than the radius of the outer walls. The outer and inner walls as well as the plate walls are perforated and comprise the filtering surfaces of the suction strainer. In accordance with first and second preferred embodiments of the present invention, the plurality of plate assemblies are preferably in the form of stacked disks that are spaced to defined troughs therebetween. In accordance with other embodiments, the plate assemblies are in other forms that increase the surface area of the suction strainer.

In accordance with preferred embodiments of the present invention, the internal core tube has a downstream end for connection to the pump suction flange and an upstream end distant from the downstream end. The internal core tube defines a longitudinal axis extending between the upstream and downstream ends. In accordance with the preferred embodiments of the present invention, a plurality of openings are defined through the side wall of the internal core tube. In accordance with certain examples of the preferred embodiments, the openings are constructed and arranged such that there is somewhat less open area near the downstream end than the upstream end, and the amount of open area tapers between the upstream end and the downstream end. As a result, when water flows into the internal core tube through the openings, a substantially uniform flow rate distribution is defined along substantially the entire length of the internal core tube.

It is therefore an object of the present invention to provide an improved BWR ECCS suction strainer.

Another object of the present invention is to increase safety by improving the operability of the ECCS of a BWR nuclear plant following a LOCA.

Yet another object of the present invention is to structurally reinforce a suction strainer sufficiently so that it can withstand the hydrodynamic forces following a LOCA in the suppression pool at a BWR nuclear plant.

Still another object of the present invention is to minimize reactive forces on the attachment ECCS piping following a LOCA.

Still another object of the present invention is to maximize the total strainer surface area within a limited geometric profile while providing a maximum strength strainer.

Still another object of the present invention is to simultaneously minimize both the thickness of collected debris on the strainer and the average entrance velocities to minimize the resultant NPSH of the ECCS following a LOCA.

Still another object of the present invention is to maximize the amount of time required to reach a particular head loss across the strainer.

Still another object of the present invention is to control the distribution of fluid flow over the strainer so as to collect debris uniformly, from disk to disk or from trough to trough, to allow scaling of the strainer for other flow rates with similar, but different size, strainers with different water flow rates.

Still another object of the present invention is to prevent vortexing and air ingestion.

Other objects, features and advantages of the present invention will become apparent upon reading and understanding this specification, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic, downstream end, perspective view of a suction strainer with an internal core tube in accordance with one example of the first preferred embodiment of the present invention.

FIG. 2 is a schematic, partially cut-away, upstream end, perspective view of the suction strainer of FIG. 1.

FIG. 3 is a schematic, side elevational view of a suction strainer with an internal core tube in accordance with one example of the second preferred embodiment of the present invention.

FIG. 4 is a schematic, upstream end, elevational view of the suction strainer of FIG. 3.

FIG. 5 is an isolated, plan view an internal core tube of the suction strainer of FIG. 3, wherein the internal core tube is in an unrolled and flattened configuration.

FIG. 6 is an isolated, schematic, elevational view of a wall of a filtering portion of the suction strainer of FIG. 3.

FIG. 7 is an isolated, plan view of a structural member of the filtering portion of the suction strainer of FIG. 3.

FIG. 8 is an isolated, schematic, plan view an outer wall of the filtering portion of the suction strainer of FIG. 3, wherein the outer wall is in an unrolled and flattened configuration.

FIG. 9 is an isolated, schematic, plan view an inner wall of the filtering portion of the suction strainer of FIG. 3, wherein the inner wall is in an unrolled and flattened configuration.

FIG. 10 is a schematic representation of portions of a BWR nuclear power plant, wherein the suction strainer of FIG. 1 is connected the ECCS of the power plant.

FIG. 11 is a schematic, side elevational view of a suction strainer with an internal core tube in accordance with an alternate embodiment of the present invention.

FIG. 12 is a schematic, upstream end, elevational view of a suction strainer with an internal core tube in accordance with another alternate embodiment of the present invention.

FIG. 13 is a schematic, side elevational view of the suction strainer of FIG. 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now in greater detail to the drawings, in which like numerals represent like components throughout the several views, FIG. 1 is a schematic, perspective view of a suction strainer 20 with a core, in accordance with the first example of the first preferred embodiment of the present invention. The core is in the form of an internal core tube 26, and the suction strainer 20 further includes an upstream end 22, an opposite downstream end 24, and an exterior filtering structure 28 connected to and at least partially bounding the internal core tube 26. In accordance with the first preferred embodiment of the present invention, the internal core tube 26 is preferably in the form of a cylinder that structurally reinforces exterior filtering structure 28. The internal core tube 26 extends between the ends 22,24 and protrudes from the filtering structure 28 at the downstream end 24. The internal core tube 26 includes a core wall 30 that encircles and defines a core chamber 32. The core wall further defines a primary opening 33 that provides access to the core chamber 32, and the longitudinal axis 34 of the suction strainer 20. The portion of the core wall 30 that is internal to the filtering structure 28 preferably defines a plurality of openings therethrough (for example, see openings 74,76,78 defined through core wall 30' in FIG. 5), as will be discussed in greater detail below. The portion of the core wall 30 that extends from the filtering structure 28 at the downstream end 24 is preferably not perforated.

The filtering structure 28 encircles a majority of the internal core tube 26 and includes an exterior filtering surface 40. FIG. 1 is schematic in nature because, as will be discussed in greater detail below, the entire filtering surface 40 is preferably perforated (i.e., the filtering surface 40 defines a plurality of openings therethrough). The perforations are not depicted in FIG. 1 in an effort to clarify the view. The filtering surface 40 further defines a plurality of protrusions such that the contour of the filtering surface 40 is varied to uniquely maximize the effective filtering area of the filtering surface 40 within a limited geometric profile described by the length and outer diameter of the suction strainer 20. The filtering structure 28 includes a plurality of spaced protrusions which cooperate to define peaks and valleys. In accordance with the first preferred embodiment of the present invention, the protrusions are in the form of plate assemblies 42a-c which are preferably in the form of circular disks, and the valleys defined between the disks are in the form of annular troughs. In accordance with the first preferred embodiment of the present invention, the disk and troughs are preferably arranged in a uniform and consistent pattern. While the suction strainer 20 is constructed in a manner that seeks to maximize its filtering surfaces 40, that construction also seeks to reduce the projected area of the suction strainer 20 such that the suction strainer 20 can withstand both high levels of hydrodynamic impact loading and minimize bending moments on the attachment piping 102 (FIG. 10).

An annular connection flange 38 encircles and is connected to the core wall 30 at the downstream end 24. The connection flange 38 is preferably constructed and arranged for attachment to a corresponding flange (not shown) in the suction line 102 (FIG. 10) of a pump 104 (FIG. 10). The connection flange 38 is depicted in simplified form in FIG. 1 in an effort to clarify the view. The connection flange 38 preferably includes a plurality of bolt holes (not shown) therethrough that facilitate connection to the corresponding flange, as should be understood by those reasonably skilled in the art. In accordance with the preferred embodiments of the present invention, the connecting flange 38 refers, for example and not limitation, to a standard bolted flange connection. In accordance with alternate embodiments of the present invention a flange 38 is not employed, and the suction strainer 20 is connected to the suction line 102 by virtue of threading, welding, or other conventional fastening techniques or devices.

When the suction strainer 20 is connected to the suction line 102 (FIG. 10) of an ECCS pump 104 (FIG. 10), liquid is drawn into the suction strainer 20 through the perforations defined through the filtering surface 40. The filtering surface 40 functions to collect solids (not shown) on the suction strainer 20. Once liquid is drawn through the filtering surface 40, the liquid is drawn through the openings (for example, see openings 74,76,78 in FIG. 5) defined through that portion of the core wall 30 that is internal to the filtering structure 28.

Referring back to the plate assemblies 42a-c, they preferably encircle the longitudinal axis 34, and the exposed surfaces of the plate assemblies 42a-c constitute a substantial portion of the filtering surface 40. The plate assemblies 42a-c include perforated plate walls 44a-f and perforated outer annular walls 46a-c that preferably encircle the longitudinal axis 34. More particularly, and representative of the construction of the plate assemblies 42b,c, the plate assembly 42a includes the plates walls 44a,b which face one another and are separated by a longitudinal distance. The plate walls 44a,b each define a peripheral edge (as an example, see peripheral edge 47 of plate wall 44' in FIG. 6), and the outer wall 46a spans and is connected between the peripheral edge of the plate wall 44a and the peripheral edge of the plate wall 44b. Each of the plate walls 44a-e define a plate hole (as an example, see plate hole 48 of plate wall 44' in FIG. 6) therethrough, and the plate holes are preferably circular and centered with respect to their respective plate wall 44a-e. The internal core tube 26 extends and is connected through the plate holes (as an example, see plate hole 48 of plate wall 44' in FIG. 6). The filtering structure 28 further includes a plurality of inner walls 43a,b. The inner walls 43a,b are preferably annular. The inner walls 43a,b are also preferably perforated such that they constitute the remainder of the filtering surface 40. The inner walls 43a,b preferably encircle the longitudinal axis 34, and the inner wall 43a is connected between the plate assemblies 42a,b while the inner wall 43b is connected between the plate assemblies 42b,c.

FIG. 2 is a schematic, partially cut-away, upstream end, perspective view of the suction strainer 20, in accordance with the first example of the first preferred embodiment of the present invention. Portions of the plate assemblies 42b,c and the inner wall 43b are cut-away to expose the portion of the internal core tube 26 that is proximate to the upstream end 22. FIG. 2 is schematic in nature by virtue of the fact that perforations are not shown extending through the plate assemblies 42a-c or the inner walls 43a,b and the openings (for example, see openings 74,76,78 in FIG. 5) that extend through the core wall 30 are not depicted in an effort to clarify the view. As mentioned above, the plate walls 44a-e each define a plate hole (for example see plate hole 48 in FIG. 6) therethrough, through which the internal core tube 26 extends and is connected. Conversely, the plate wall 44f, which is partially cut-away in FIG. 2, does not define such a plate hole such that the plate wall 44f functions to cover the upstream end 22 of the internal core tube 26 and the core chamber 32. Except for that difference between the plate wall 44f and the other plate walls 44a-e, the plate assembly 42c is representative of the plate assemblies 42a,b.

In accordance with the first preferred embodiment of the present invention, the internal core tube 26 functions as a structural member that supports the filtering structure 28. The filtering structure 28 and the internal core tube 26 are interconnected in a manner that synergistically strengthens the suction strainer 20. In accordance with the first preferred embodiment of the present invention, the strengthening is enhanced by a plurality of structural members 50 that are preferably rectangular and planar. The structural members 50 are disposed within and are effectively part of each of the plate assemblies 42a-c. Some of the structural members 50 are cut-away in FIG. 2 to clarify the view. In accordance with the first preferred embodiment of the present invention, the strengthening is also enhanced by a plurality of shorter structural members 52 that are preferably rectangular and planar. Structural members 52 are associated with each of the inner walls 43a,b. In accordance with the first preferred embodiment of the present invention, the structural members 50,52 are solid. In accordance with alternate embodiments of the present invention, holes or other perforations are defined through the structural members 50,52. In accordance with the first preferred embodiment of the present invention, the solid structural members 50,52 function to both structurally reinforce the filtering structure 28 and prevent vortexing and air ingestion.

More particularly, and representative of the construction of the plate assemblies 42a,b, the structural members of plate assembly 42c extend radially from the core wall 30 and are angularly displaced about the longitudinal axis 34. Each of the structural members 50 includes an inner edge (for example, see inner edge 54 of structural member 50' in FIG. 7) connected to the core wall 30, an opposite outer edge (for example, see outer edge 56 in FIG. 7) connected to the outer annular wall 46c, a side edge (for example, see side edge 58 in FIG. 7) connected to the plate wall 44f, and an opposite side edge (for example, see side edge in FIG. 7) connected to the plate wall 44e. Further, and representative of the plate assemblies 42a,b, the plate assembly 42c defines an annular plate chamber 62 that is bound by the core wall 30, the outer annular wall 46c, the plate wall 44f, and the plate wall 44e.

The inner wall 43b is representative of the inner wall 43a. The inner wall 43b is connected to a plurality of the structural members 52, wherein the structural members 52 extend radially from the core wall 30 and are angularly displaced about the longitudinal axis 34. Each of the structural members 52 is similar to but sized differently from the structural members 50. Each of the structural members 52 associated with the inner wall 43b include an inner edge connected to the core wall 30, an opposite outer edge connected to the inner wall 43b, a side edge connected to the plate wall 44e, and an opposite side edge connected to the plate wall 44d. (For example, see the inner edge 54, outer edge 56, side edge 58, and side edge 60 of the structural member 50' in FIG. 7.) Further, and representative of the inner wall 43a, the inner wall 43b defines an intermediate chamber 64 that is bounded by the core wall 30, the inner wall 43b, inner portions of the plate wall 44e, and inner portions of the plate wall 44d. In accordance with the first preferred embodiment of the present invention, each of the plate assemblies 42a-c define plate chambers 62 and each of the inner walls 43a,b define intermediate chambers 64, and all of the chambers 62,64 comprise a filter chamber 66. Stated differently, the filter chamber 66 is defined between the core wall 30 and the filtering surface 40 of the filtering structure 28.

As discussed in greater detail below with reference to a first example of the second preferred embodiment of the present invention, in accordance with the first example of the first preferred embodiment of the present invention, the openings defined through the core wall 30 (for example, see openings 74,76,78 defined through core wall 30' in FIG. 5) are uniquely constructed and arranged so that a substantially controlled inflow distribution, which is preferably uniform, is defined along the length of the internal core tube 26 that is internal to the filtering structure 28. A uniform inflow distribution seeks to, among other things, collect the debris on the filtering surface 40 uniformly, from disk to disk or trough to trough, and thereby allow scaling of test results to strainers with different flow rates and different surface areas. This flow pattern control also seeks to assist in preventing vortexing and air ingestion at the suction strainer 20. In accordance with other examples of the first preferred embodiment, the openings defined through the core wall 30 are constructed and arranged so that the internal core tube 26 does not seek to control the inflow distribution.

FIG. 3 is a schematic, side elevational view of a suction strainer 20' in accordance with a first example of the second preferred embodiment of the present invention. The suction strainer 20' of the first example of the second preferred embodiment is very similar, in general terms, to the suction strainer 20 (FIGS. 1 and 2) of the first example of the first preferred embodiment. Thus, except where specific differences between the suction strainer 20' and the suction strainer 20 are noted or apparent, the following disclosure of the suction strainer 20' should be considered as a supplement to the foregoing disclosure of the suction strainer 20, and visa versa.

In accordance with the second preferred embodiment of the present invention, the internal core tube 26' of the suction strainer 20' is preferably cylindrical and longer than the internal core tube 26 (FIGS. 1 and 2) of the first embodiment. Further, the suction strainer 20' includes more inner walls 43'a-e and plate assemblies 42'a-f than the suction strainer 20 (FIGS. 1 and 2) of the first preferred embodiment. The plate assemblies 42'a-f include plate walls 44'a-l. The inner walls 43'a-e and plate assemblies 42'a-f preferably encircle the internal core tube 26', as is indicated by the broken line showing of the internal core tube 26'. FIG. 3 is schematic in nature because, while the inner walls 43'a-e and plate assemblies 42'a-f preferably define a multiplicity of apertures therethrough, those apertures are not depicted in FIG. 3 in an effort to clarify the view. In accordance with the second preferred embodiment of the present invention, the internal core tube 26' is preferably in the general form of a cylinder that structurally reinforces exterior filtering structure 28'.

In accordance with the second preferred embodiment of the present invention, the suction strainer 20' defines an overall length that is represented by the dimension "a". The core wall 30' defines a first length that does not define openings 74,76,78 (FIG. 5) therethrough, and that first length is represented by the dimension "b". The core wall 30' further defines a second length, represented by the dimension "c", that does define openings 74,76,78 (FIG. 5) therethrough and that is surrounded by the plate assemblies 42'a-f and the inner walls 43'a-e. A separation distance, represented by the dimension "d", is defined between each of the plate assemblies 42'a-f. Also, each of the plate assemblies 42'a-f individually define a thickness that is represented by the dimension "e". The internal core tube 26', inner walls 43'a-e, and plate assemblies 42'a-f define diameters that are represented by the dimensions "f", "g", and "h", respectively. In accordance with one acceptable example of the second preferred embodiments, and in approximation, the dimension "a" is acceptably 36.0 inches, the dimension "b" is acceptably 3.375 inches, the dimension "c" is acceptably 29.875 inches, the dimension "d" is acceptably 2.0 inches, the dimension "e" is acceptably 3.313 inches, the dimension "f" is acceptably 24.0 inches, the dimension "g" is acceptably 26.0 inches, and the dimension "h" is acceptably 42.0 inches.

As suggested by the broken line showing of the core wall 30' in FIG. 3, in accordance with the second preferred embodiment of the present invention, each of the plate walls 44'a-k defines a centered plate hole 48 (FIG. 6) therethrough. The internal core tube 26' extends through the plate holes 48. As an exception, however, the plate wall 44'l does not define such a hole 48 and therefore covers the upstream end 22' of the internal core tube 26' and the core chamber (for example see the core chamber 32 of FIGS. 1 and 2). The plate wall 44'l is more fully depicted in FIG. 4, which is a schematic, upstream end, elevational view of the suction strainer 20', in accordance with the first example of the second preferred embodiment of the present invention. The fact that the plate wall 44'l covers the upstream end 22' of the internal core tube 26' is indicated by the broken line showing of the core wall 30' in FIG. 4.

In accordance with the second preferred embodiment of the present invention, each of the plate assemblies 42'a-f (FIG. 3) include a plurality of structural members 50' therein; and the arrangement and configuration of the structural members 50' within the plate assembly 42'f is representative of the configuration and arrangement of the structural members 50' within each of the plate assemblies 42'a-e. As indicated by the broken line showing of the structural members 50' in FIG. 4, the structural members 50' extend radially from and are angularly displaced about the internal core tube 26'. In accordance with the second preferred embodiment, an identical angle "φ" is defined between each adjacent structural member 50', and one acceptable example of the angle "φ" is 60 degrees. In accordance with the second preferred embodiment of the present invention, the inner walls 43'a-e are not reinforced by structural components that correspond to the structural members 52 (FIG. 2) of the first preferred embodiment. However, in accordance with alternate embodiments of the present invention the inner walls 43'a-e are reinforced by structural components that correspond to the structural members 52 (FIG. 2) of the first preferred embodiment.

FIG. 5 is an isolated, plan view of the core wall 30' in accordance with the first example of the second preferred embodiment of the present invention, wherein the core wall 30' is in an unrolled and flattened configuration. The core wall 30' includes opposite wall edges 68,70 that are preferably joined together in a manner that creates the cylindrical internal core tube 26' (FIG. 3). The internal core tube 26' further includes an upstream edge 71 to which the plate wall 44'l (FIGS. 3 and 4) is affixed. Broken lines 72a-k are included in FIG. 5 for explanatory purposes only. The lines 72a-k represent the points at which the inner peripheral edges 73 (FIG. 6) of the plate walls 44a-k (FIG. 3), respectively, contact the core wall 30' when the plate walls 44a-k are properly installed on the cylindrical internal core tube 26' (FIG. 3).

In accordance with the first example of the second preferred embodiment of the present invention, the openings 74,76,78, only a few of which are specifically pointed out in FIG. 5 in an effort to clarify the view, are in the form of circular holes which extend through the core wall 30'. Also, in accordance with the second preferred embodiment of the present invention, open areas are defined through the core wall 30' by virtue of the openings 74,76,78. Each individual opening 74,76,78 represents or defines an open area. The open area of an individual opening 74,76,78 is representative of the capacity of that individual opening 74,76,78 to pass liquid. Thus, the open area can acceptably be measured perpendicular to the direction of liquid flow through the most restrictive portion of an opening 74,76,78. In accordance with the first example of the second preferred embodiment of the present invention, the openings 78 are the only type of openings defined between the lines 72h and the upstream end 22' of the core wall 30', the openings 76 are the only type of openings defined between the lines 72d,h, and the openings 74 are the only type of openings defined between the lines 72a,d.

Unit areas consisting of a portion of the core wall 30' can be considered to define open areas, wherein the open area of a unit area is the summation all of the individual open areas defined within that unit area. Accordingly, and for example and not limitation, a plurality of core units can be defined as extending sequentially along the length of the internal core tube 26' (FIG. 3). In accordance with one acceptable example of such a sequential arrangement of core units, a first unit of the plurality of units can acceptably and hypothetically be identified as being that portion of the core wall 30' defined between the lines 72b,d. That first unit defines a first unit open area equal to the summation of the open areas of each of the openings 74 defined between the lines 72b,d. Similarly, a second unit of the plurality of units can acceptably and hypothetically be identified as being that portion of the core wall 30' defined between the lines 72d,f. That second unit defines a second unit open area equal to the summation of the open areas of each of the openings 76 defined between the lines 72d,f. In accordance with the first example of the second preferred embodiment of the present invention, the first unit open area is smaller than the second unit open area such that when a pump draws liquid through the wall 30' of the internal core tube 26' (FIG. 3), the flow (i.e., inflow) of liquid through the first unit is substantially similar to the inflow of liquid through the second unit. The lines 72a-k are used in the foregoing example only because they aid in the explanation of the concept of core units. The lines 72a-k are not intended to and should not limit the hypothetical configuration of core units. Core units can be conceptualized and defined without any reference to the lines 72a-k. For example and not limitation, it is acceptable for the edge of a core unit to be located at any location between neighboring lines 72.

As evidenced by the foregoing, in accordance with the first example of the second preferred embodiment of the present invention, the openings 74,76,78 are constructed and arranged such that less open area is defined near the downstream end 24' (FIG. 3) than the upstream end 22' (FIG. 3). Thus, when liquid is drawn into the core chamber (for example see the core chamber 32 of FIGS. 1 and 2) by a pump or the like, a substantially uniform flow (i.e., inflow) distribution is defined along the length of the internal core tube 26' (FIG. 3). In accordance with the first example of the second preferred embodiment of the present invention, the variation in open area of the core wall 30' (e.g., the variation in the open area of the internal core tube 26') is achieved by varying the sizing of the openings 74,76,78. In other words, in accordance with the first example of the second preferred embodiment of the present invention, the pattern of the openings 74,76,78 does not vary significantly along the length of the core wall 30'. More particularly, the opening pattern defined between the lines 72a,b is repeated between the lines 72c,d, the lines 72e,f, the lines 72g,h, the lines 72i,j, and the line 72k and the upstream end 22' of the core wall 30'. Similarly, the opening pattern defined between the lines 72b,c is repeated between the lines 72d,e, the lines 72f,g, the lines 72h,i, and the lines 72j,k. Accordingly, in accordance with the first example of the second preferred embodiment of the present invention, the variation in open area is achieved by virtue of the fact that the openings 78 (which are preferably the only type of openings defined between the lines 72h and the upstream end 22' of the core wall 30') are larger than the openings 74; and the openings 74 (which are preferably the only type of openings defined between the lines 72d,h) are larger than the openings 72 (which are preferably the only type of openings defined between the lines 72a,d). In accordance with first example of the second preferred embodiment of the present invention, each of the openings 74 acceptably defines a diameter of approximately 0.875 inches, each of the openings 76 defines a diameter of approximately 1.063 inches, and each of the openings 78 defines a diameter of approximately 1.25 inches. Also in accordance with the first example of the second preferred embodiment of the present invention, the core wall 30' is acceptably constructed from a sheet of steel such as, but not limited to, a piece of quarter inch coated A36 carbon or uncoated stainless steel.

As mentioned above, in accordance with the first example of the second preferred embodiment of the present invention the variations in open area along the length of the internal core tube 26' (FIGS. 3 and 4) are established by repeating the pattern of openings but varying the size of the openings defined through the core wall 30'. However, in accordance with alternate embodiments of the present invention all of the openings defined through the core wall 30' are the same size, and the variations in open area along the length of the internal core tube 26' (FIG. 3) are established by varying the pattern of the openings through the core wall 30'. In other words, in accordance with alternate embodiments of the present invention, the variation in open area exists by virtue of the fact that more openings are defined through the core wall 30' proximate to the upstream end 22' (FIG. 3) of the internal core tube 26'. Also, in accordance with other examples of the second preferred embodiment, the open areas through the core wall 30' are substantially uniform along the length of the internal core tube 26', whereby uniform inflow along the length of the internal core tube 26' is not provided.

FIG. 6 is an isolated, schematic, elevational view of a plate wall 44' that is representative of the plate walls 44'a-k (FIG. 3), in accordance with the second preferred embodiment of the present invention. The plate wall 44' includes an outer peripheral edge 47 and an inner peripheral edge 73 that encircles and defines a central plate hole 48. The internal core tube 26' (FIG. 3) extends through the central plate holes 28 of the plate walls 44'a-k (FIG. 3). The plate wall 44' depicted in FIG. 6 is not representative of the plate wall 44l (FIG. 3) because the plate wall 44'l does not define a plate hole 48 therethrough, as mentioned above.

FIG. 6 is schematic in nature because each of the plate walls 44'a-l (FIG. 3) define a multiplicity of perforations therethrough that are preferably evenly distributed. The perforations are not clearly shown in FIG. 6 in an effort to clarify the view, however a sampling of the perforations is schematically represented by dots. In accordance with the second preferred embodiment of the present invention, an acceptable size of each individual perforation is within the range of approximately 0.0625 inches to approximately 0.250 inches. In accordance with one acceptable example, the perforations are so sized and so numerous that each of the plate walls 44'a-l is approximately forty percent open area. Also, the plate walls 44'a-l are acceptably constructed from a material such as, but not limited to, eleven gauge carbon or stainless steel. In accordance with an alternate embodiment of the present invention, the portion of the plate wall 44'l (FIG. 3) that covers the upstream end of the core chamber (for example see core chamber 32 in FIG. 2) is not perforated.

The term "percent open area" as used within this disclosure can be explained with reference to the plate wall 44'. For example, before the plate wall 44' is perforated it is zero percent open, whereas after the plate wall 44' is perforated it includes a multiplicity of perforations such that the plate wall 44' defines an open area. Each individual perforation represents or defines an open area which is representative of the capacity of that perforation to pass liquid, as discussed above. Further, unit areas consisting of a portion of the plate wall 44' can be considered to define an open area, wherein the open area of a unit area is the summation all of the individual open areas defined within that unit area. For example, if a one square inch surface area of the plate wall 44' is identified before the plate wall 44' is perforated, that square inch surface area is zero percent open. After the plate wall 44' is perforated and that one square inch surface area includes a plurality of perforations therethrough, that square inch surface area is some percent open. If the sum of all of the open areas in that one square inch surface add up to an area of 0.4 square inches, then that square inch surface area is forty percent open. If the entire plate wall 44' is perforated in a manner substantially similar to that one square inch, the plate wall 44' is forty percent open.

FIG. 7 is an isolated, elevational view of a structural member 50' in accordance with the second preferred embodiment of the present invention. In accordance with the second preferred embodiment of the present invention, the structural members 50' are solid. In accordance with the second preferred embodiment of the present invention, the solid structural members 50' function to both structurally reinforce the filtering structure 28' (FIG. 3) and prevent vortexing. In accordance with alternate embodiments of the present invention, a plurality of holes are defined through the structural members 50'. The holes seek to equalize flow within the filter chamber (for example, see the filter chamber 66 in FIG. 2).

In accordance with the second preferred embodiment of the present invention, structural members 50' are incorporated into each of the plate assemblies 42'a-f (FIG. 3). Each of the structural members 50' extends radially from the core wall 30' (FIG. 3). Further, structural members 50' within a single plate assembly 42' are, in accordance with the second preferred embodiment, angularly displaced about the longitudinal axis 34' (FIG. 3) as depicted in FIG. 4. In accordance with various alternate embodiments of the present invention, each plate assembly 42' preferably includes six or more structural members 50' angularly displaced about the longitudinal axis 34'. Each of the structural members 50' includes an inner edge 54 connected to the internal core tube 26' (FIG. 3), an opposite outer edge 56 connected to the respective outer wall 46' (FIG. 3), a side edge 58 connected to the one plate wall 44' (FIGS. 3 and 6), and an opposite side edge 60 connected to another plate wall 44'. In accordance with the second preferred embodiment of the present invention the structural members 50' are acceptably constructed from a sheet of steel such as, but not limited to, a piece of eighth-inch carbon or stainless steel. In accordance with the second preferred embodiment of the present invention, structural members 52 (FIG. 2) are not employed. In accordance with an alternate embodiment of the present invention, structural members 52 are employed.

FIG. 8 is an isolated, schematic, plan view of an representative outer wall 46' of a plate assembly 42' (FIG. 3), wherein the outer wall 46' is in an unrolled and flattened configuration in accordance with the second preferred embodiment of the present invention. The outer wall 46' includes opposite short edges 80,82 that are preferably connected such that the outer wall 46' encircles the longitudinal axis 34' (FIG. 3). The outer wall 46' further includes opposite elongated side edges 84,86. In a representative plate assembly 42' (FIG. 3), the elongated edge 84 of the outer wall 46' is connected to the outer peripheral edge 47 (FIG. 6) of one of the plate walls 44', and the other elongated edge 86 of the outer wall 46' is connected to the outer peripheral edge 47 of the other plate wall 44'.

FIG. 9 is an isolated, schematic, plan view a representative inner wall 43' of the suction strainer 20' (FIG. 3), wherein the inner wall 43' is in an unrolled and flattened configuration in accordance with the second preferred embodiment of the present invention. The inner wall 43' includes opposite short edges 88,90 that are preferably connected such that the inner wall 43' encircles the longitudinal axis 34' (FIG. 3). The inner wall 43' further includes opposite elongated edges 92,94. With respect to an exemplary inner wall 43', the elongated edge 92 is connected to one plate wall 44' (FIG. 3) while the other elongated edge 94 is connected to another plate wall 44'.

FIGS. 8 and 9 are schematic in nature because each of walls 43',46' define a multiplicity of perforations therethrough that are preferably evenly distributed. The perforations are not clearly shown in FIGS. 8 and 9 for the sake of clarity, however a sampling of the perforations is schematically represented by dots. In accordance with the second preferred embodiment of the present invention, and with respect to the inner walls 43'a-e (FIG. 3) and outer walls 46'a-f (FIG. 3), an acceptable size for each individual perforation is within the range of approximately 0.0625 inches to approximately 0.125 inches. In accordance with one acceptable example, the perforations through the walls 43'a-e,46'a-f are so sized and so numerous that each of the walls 43'a-e,46'a-f are approximately forty percent open. In accordance with the second preferred embodiment of the present invention, the walls 43',46' are acceptably constructed, for example and not limitation, from a sheet of metal such as, but not limited to, a piece of eleven gauge carbon or stainless steel. In accordance with alternate embodiments of the present invention, the walls 43'a-e,46'a-f are acceptably constructed, for example and not limitation, from wire wrapped well screen.

Referring to FIG. 10, which is a schematic representation of portions of a BWR nuclear power plant, in accordance with the preferred embodiments of the present invention, the suction strainer 20 (FIGS. 1 and 2) and the suction strainer 20' (FIGS. 3 and 4) are preferably connected to an ECCS of a BWR nuclear power plant. FIG. 10 depicts a portion of an ECCS following a LOCA. The suction strainer 20 is submerged in a suppression pool 100, where the suction strainer 20 is connected to the downstream end of a suction line 102 through which an ECCS pump 104 draws water 105 from the suppression pool 100. In one mode of operation (which is generally depicted in FIG. 10), the ECCS pump 104 discharges through a discharge line 106 to a reactor core 108. In another mode of operation, the ECCS pump 104 discharges back to the suppression pool 100. The suction strainers 20,20' are uniquely constructed and arranged, and operate, such that they are capable of being readily incorporated into, optimize the operation of, and are capable of withstanding the rigors associated with, ECCSs.

It should be understood that the specific construction and arrangements of the suction strainer 20 (FIGS. 1 and 2) and the suction strainer 20' (FIGS. 3 and 4) are provided as acceptable examples only. The broad concepts disclosed with respect to the suction strainer 20 and the suction strainer 20' lend themselves to a variety of differently configured suction strainers, and configurations will vary depending upon desired flow rates, space constraints, and the hydrodynamic forces that a particular suction strainer and the attachment ECCS piping will be potentially subjected to. For example, FIG. 11 is a schematic, side elevational view of a suction strainer 20" in accordance with an alternate embodiment of the present invention. The suction strainer 20" depicted in FIG. 11 is substantially similar to the suction strainer 20' of the second preferred embodiment, except that it includes less plate assemblies 42"a-d, and the diameters of the plate assemblies 42"a-d taper. As another example, FIG. 12 is a schematic, upstream end, elevational view of a suction strainer 20'", in accordance with another alternate embodiment of the present invention. FIG. 13 is a schematic, side elevational view of the suction strainer 20'" of FIG. 12. The suction strainer 20'" depicted in FIGS. 12 and 13 is substantially similar to the suction strainer 20' of the second preferred embodiment, except that the suction strainer 20'" includes less plate assemblies 42"a-d, and the plate assemblies 42'"a-d are starshaped. The plate assemblies 42'" encircle the internal core tube 26", as is indicated by the broken line showing of the internal core tube 26" and core wall 30" in FIG. 12.

As an additional example, another embodiment of the present invention includes a convertible suction strainer (not shown) that includes a 170 square foot filtering surface (for example see the filtering surface 40 in FIGS. 1 and 2), 13 disks (for example see the plate assemblies 42 in FIGS. 1 and 2) that are 40 inches in diameter, and a 24 inch flange (for example see the connection flange 38 of FIG. 1), wherein the convertible suction strainer is 48 inches long from the first to the last disk. The internal core tube (for example see the internal core tube 26 in FIGS. 1 and 2) of the convertible suction strainer has large evenly spaced holes therethrough that are not constructed and arranged to control inflow through the internal core tube. The internal core tube of the convertible suction strainer is constructed and arranged to structurally support a filtering structure (for example see the filtering structure 28 in FIGS. 1 and 2) that is connected to and extends radially from the internal core tube. The downstream end of the internal core tube of the convertible suction strainer is covered with a perforated plate (for example see the plate wall 44'l in FIG. 3) that can be temporarily opened to provide an opening to the core chamber that is defined by the internal core tube (i.e., the first internal core tube). A second internal core tube is capable of being inserted through the provided opening so that it is installed within the core chamber of the first internal core tube. The second internal core tube is constructed and arranged to control the inflow of water, in the manner discussed above, such that substantially even inflow is established along the length of the first internal core tube.

While the embodiments of the present invention which have been disclosed herein are the preferred forms, other embodiments of the method and apparatus of the present invention will suggest themselves to persons skilled in the art in view of this disclosure. Therefore, it will be understood that variations and modifications can be effected within the spirit and scope of the invention and that the scope of the present invention should only be limited by the claims below. It is also understood that any relative relationships and dimensions shown on the drawings are given as preferred relative relationships and dimensions, but the scope of the invention is not to be limited thereby. 

We claim:
 1. In a boiling water nuclear power plant wherein a discharge line provides fluid communication between an emergency core cooling pump and a reactor core and a suction line provides fluid communication between the emergency core cooling pump and a suppression pool, wherein a suction strainer is connected to the suction line for removing solids from a flow of liquid being drawn into the suction line, and wherein the improvement comprises:said suction strainer includingan internal member including a first end and a second end, and defining a length between said first end and said second end, said internal member further including an internal wall defining an internal chamber that is at least partially bounded by said internal wall,a primary opening at said second end that is open to said internal chamber, and through which the liquid is drawn from said internal chamber into the suction line of the pump, and a plurality of internal apertures that extend through said internal wall and define open areas through which the liquid is drawn into said internal chamber; and an external member connected to said internal member and including an external wall,wherein said external wall and said internal wall cooperate to substantially bound and define an external chamber, wherein the liquid is drawn from said external chamber into said internal chamber through said plurality of internal apertures, and wherein said external wall defines a plurality of external apertures through which liquid is drawn into said external chamber; said internal member being constructed and arranged such that said internal member provides substantial structural reinforcement to said external member; and a plurality of structural members angularly displaced about said internal member and extending radially from said internal member to said external wall of said external member, wherein said plurality of structural members provide substantial structural reinforcement to said external member, and wherein said external wall further defines a surface area and a plurality of protrusions that tend to increase said surface area.
 2. The suction strainer of claim 1, wherein said open areas increase toward said first end such that the flow of liquid into said internal chamber through said plurality of apertures is substantially uniform along at least a substantial portion of said length of said internal member.
 3. The suction strainer of claim 1, wherein said plurality of protrusions define a plurality of alternating peaks and valleys that extend along said length of said internal member.
 4. The suction strainer of claim 1, wherein said external wall extends around said internal member and said plurality of protrusions define a plurality of alternating peaks and valleys that extend around said internal member.
 5. In a boiling water nuclear power plant wherein a discharge line provides fluid communication between an emergency core cooling pump and a reactor core and a suction line provides fluid communication between the emergency core cooling pump and a suppression pool, wherein a suction strainer is connected to the suction line for removing solids from a flow of liquid being drawn into the suction line, and wherein the improvement comprises:said suction strainer includingan internal member including a first end and a second end, and defining a length between said first end and said second end, said internal member further including an internal wall definingan internal chamber that is at least partially bounded by said internal wall, a primary opening at said second end that is open to said internal chamber, and through which the liquid is drawn from said internal chamber into the suction line of the pump, and a plurality of internal apertures that extend through said internal wall and define open areas through which the liquid is drawn into said internal chamber; andan external member connected to said internal member and including an external wall,wherein said external wall and said internal wall cooperate to substantially bound and define an external chamber, wherein the liquid is drawn from said external chamber into said internal chamber through said plurality of internal apertures, and wherein said external wall defines a plurality of external apertures through which liquid is drawn into said external chamber, a surface area, and a plurality of protrusions that tend to increase said surface area, and plurality of plate assemblies that surround said internal member and are spaced sequentially along said length of said internal member, wherein adjacent plate assemblies of said plurality of plate assemblies are longitudinally displaced such that open areas are defined between said adjacent plate assemblies.
 6. The suction strainer of claim 5, wherein each plate assembly of said plurality of plate assemblies inches a pair of plate walls, wherein each wall of said pair of plate walls is connected to, surrounds, and extends radially from said internal member, wherein a first wall of said pair of plate walls is longitudinally displaced from a second wall of said pair of plate walls such that said pair of plate walls define a plate chamber therebetween, and wherein each wait of said pair of plate walls defines a first plurality of plate apertures therethrough that are open to said plate chamber, and a first wall extending around and distant from said internal member, connected to and spanning between said pair of plate walls, and defining a second plurality of plate apertures therethrough that are open to said plate chamber.
 7. The suction strainer of claim 6, wherein said internal member is cylindrical, wherein each plate assembly of said plurality of plate assemblies is disk shaped, and wherein said first wall of each plate assembly of said plurality of plate assemblies encircles said internal member.
 8. The suction strainer of claim 5, wherein said internal member is cylindrical.
 9. The suction strainer of claim 5, wherein said first end of said internal member is closed, whereby there is no opening to the internal chamber through the first end.
 10. In a boiling water nuclear power plant wherein a discharge line provides fluid communication between an emergency core cooling pump and a reactor core and a suction line provides fluid communication between the emergency core cooling pump and a suppression pool, wherein a suction strainer is connected to the suction line for removing solids from a flow of liquid being drawn into the suction line, and wherein the improvement comprises:said suction strainer includingan internal member including a first end and a second end, and defining a length between said first end and said second end, said internal member further including an internal wall defininga longitudinal axis, an internal chamber extending along said longitudinal axis, said internal chamber being at least partially bounded by said internal wall, a primary opening at said second end that is open to said internal chamber, and through which the liquid is drawn from said internal chamber into the suction line of the pump, and a plurality of internal apertures that extend through said internal wall and define open areas through which the liquid is drawn into said internal chamber; and an external member connected to said internal member and including an external wall,wherein said external wall and said internal wall cooperate to substantially bound and define an external chamber, wherein the liquid is drawn from said external chamber into said internal chamber through said plurality of internal apertures, wherein said external wall defines a plurality of external apertures through which liquid is drawn into said external chamber, and wherein said external member is structurally supported by said internal member and wherein said external wall further defines a plurality of disks spaced sequentially along said length of said internal member, wherein each disk of said plurality of disks includes a pair of disk walls, wherein each wall of said pair of disk walls is connected to, encircles, and extends radially from said internal member for a complete revolution about said longitudinal axis to define a peripheral edge displaced from and encircling said internal member, wherein a first wall of said pair of disk walls is longitudinally displaced from a second wall of said pair of disk walls such that said pair of disk walls define a disk chamber therebetween, and wherein each wall of said pair of disk walls defines a first plurality of disk apertures therethrough that are open to said disk chamber, and an outer wall encircling said internal member, connected to and spanning between said peripheral edges of said pair of disk walls, and defining a second plurality of disk apertures therethrough that are open to said disk chamber, and wherein adjacent disks of said plurality of disks are longitudinally displaced such that an open area is defined between adjacent disks of said plurality of disks.
 11. The suction strainer of claim 10, wherein the internal wall further defines a plurality of core units of substantially equal length and extending sequentially along said length of said internal member, wherein each unit of said plurality of core units defines a unit open area, wherein said unit open area of an individual unit of said plurality of core units is equal to the sum of said open areas within said individual unit, and wherein a first unit of said plurality of core units defines a first unit open area and a second unit of said plurality of core units that is interposed between said first unit and said downstream end defines a second unit open area, wherein said first unit open area is greater than said second unit open area.
 12. The suction strainer of claim 11, wherein each unit of said plurality of core units encircles a segment of said longitudinal axis, and wherein said open area of an individual aperture of said plurality of internal apertures is measured perpendicular to the direction of liquid flow through said individual aperture.
 13. The suction strainer of claim 12, wherein said external member further includes a plurality of inner wails encircling said internal member and spanning between adjacent disks of said plurality of disks.
 14. The suction strainer of claim 13, wherein said outer walls define an outer radius from said longitudinal axis, and wherein said plurality of inner walls define an inner radius from said longitudinal axis, wherein said outer radius is greater than said inner radius.
 15. The suction strainer of claim 13, wherein the suction strainer further comprises a flange connected to said second end of said internal member and encircling said primary opening.
 16. The suction strainer of claim 12, wherein disks of said plurality of disks further include a plurality of structural members, wherein in each disk of said plurality of disks that includes structural members of said plurality of structural members, said structural members are angularly displaced about said internal member and extend radially between said internal wall and said outer wall.
 17. The suction strainer of claim 16, wherein in each disk of said plurality &disks that includes structural members of said plurality of structural members, said structural members further span between said a pair of disk walls.
 18. In a boiling water nuclear power plant wherein a suction line connected to a core cooling pump provides fluid communication between the reactor core and liquid stored in the suppression pool of the plant, wherein a suction strainer is connected to the suction line for removing solids from a flow of liquid being drawn into the suction line, and wherein the improvement comprises:said suction strainer includingan external filtering structure having a plurality of perforations therethrough said external filtering structure defining a surface area, and a plurality or protrusions that increase said surface area; an internal core tube connected to and disposed at least partially within said external filtering structure, said internal core tube constructed and arranged to provide primary structural support for said suction strainer, said core tube having a first end and a second end and including a core wall extending between said first end and said second end of said core tube, said core wall defining a plurality of openings therethrough and an internal chamber at least partially bounded by said core wall, said second end of said core tube being constructed and arranged to mate with the suction line and defining a primary opening to permit fluid communication between said internal chamber and the suction line, wherein the liquid is drawn into said external filtering structure through said plurality of perforations, and wherein the liquid is further drawn into said internal chamber through said plurality of openings defined in said core wall; and a plurality of structural members connecting the core wall of said core tube to said external filtering structure, said structural members being angularly displaced about the core wall of said core tube and extending radially from the core wall to said external filtering structure to provide structural reinforcement to said external filtering structure.
 19. The suction strainer of claim 18, wherein the plurality of openings through said core wall define open areas that increase in size toward said first end of said core tube such that the flow of liquid drawn into said internal chamber through said plurality of openings is substantially uniform along a substantial portion of said suction strainer, whereby the operation of said external filtering structure is enhanced.
 20. The suction strainer of claim 18 wherein said suction strainer further comprises a flange connected to said second end of said core tube and disposed around said primary opening.
 21. The suction strainer of claim 18 wherein the plurality of protrusions define a plurality of alternating peaks and valleys that extend along said internal core tube between said first and second ends thereof.
 22. The suction strainer of claim 21, wherein said plurality of protrusions are in the form of a plurality of plate assemblies that surround said internal core tube, wherein adjacent plate assemblies of said plurality of plate assemblies are longitudinally displaced such that open areas are defined between said adjacent plate assemblies.
 23. The suction strainer of claim 18, wherein said internal core tube is cylindrical in shape.
 24. In a boiling water nuclear power plant wherein a suction line connected to a core cooling pump provides fluid communication between the reactor core and liquid stored in the suppression pool of the plant, wherein a suction strainer is connected to the suction line for removing solids from a flow of liquid being drawn into the suction line, and wherein the improvement comprises:said suction strainer including an internal core tube constructed and arranged to provide primary structural support for said suction strainer, said core tube having a first end and a second end and including a core wall extending between said first end and said second end of said core tube, said core wall defining a plurality of openings therethrough and an internal chamber at least partially bounded by said core wall, said second end of said core tube being constructed and arranged to mate with the suction line and defining a primary opening to permit fluid communication between said internal chamber and the suction line, wherein the liquid is drawn into said internal chamber through said plurality of openings; an external filtering structure spaced from, connected to and at least partially bounding said internal core tube, said external filtering structure defining a surface area in the form of a plurality of protrusions, and including a plurality of perforations through which the liquid from the suppression pool is drawn; and a plurality of structural members connecting the core wall of said core tube to said external filtering structure, said structural members extend radially from and are connected to the core wall of said core tube, and are angularly displaced about the core wail of said core tube to provide structural reinforcement to said external filtering structure. 